The subject matter disclosed herein relates to gas turbine engines, and more particularly to temperature management therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gas that flows downstream through multiple turbine stages. A turbine stage includes a stationary turbine nozzle having stator vanes that guide the combustion gas through a downstream row of turbine rotor blades extending radially outwardly from a supporting disk, which is powered by extracting energy from the hot combustion gas.
A first stage turbine nozzle receives hot combustion gas from the combustor, which is subsequently directed to the first stage turbine rotor blades, for extraction of energy therefrom. A second stage turbine nozzle may be disposed downstream of the first stage turbine rotor blades, and is followed in turn by a row of second stage turbine rotor blades, for extraction of additional energy from the combustion gas. Similarly, a third stage turbine nozzle may be disposed downstream of the second stage turbine rotor blades, and is followed in turn by a row of third stage turbine rotor blades.
As energy is extracted from the hot combustion gas, the temperature of the gas is correspondingly reduced. However, since the gas temperature is relatively high, the turbine stages are typically cooled by delivery of a coolant, such as compressed air which may be diverted from the compressor. Since the diverted cooling air is unavailable to the combustor, the overall efficiency of the engine is correspondingly reduced. It is therefore desired to improve the use of such cooling air for improving the overall efficiency of the engine.
The quantity of cooling air required is dependant on the temperature of the combustion gas, material selection and turbine engine design. That temperature varies from idle operation of the turbine engine to high power operation, and from low to high temperatures at the compressor inlet. For example, in a land-based gas turbine engine that powers an electrical generator, high temperature operating conditions typically occur during the hot day, peak power condition. Combustion gas temperature may therefore vary temporally over the operating or running conditions of the engine. Since combustion gas temperature directly affects the durability of the vanes and blades, the cooling air requirement for the turbine stages must be effective for withstanding high combustion gas temperature operation of the engine, although that running condition may only occur for a relatively short time during engine operation.
A wheel space is defined between the first stage nozzle assembly and the compressor exit diffuser. Due to its proximate location to the outlet of the combustor, the wheel space is subject to some of the higher temperatures experienced by the turbine. To maintain the wheel space within a temperature range which is suitable for the long term durability of the components in that region, cooling air is delivered to the wheel space. Under certain operating conditions, such as high ambient temperatures resulting in high temperatures at the inlet of the compressor, the volume of cooling air may be insufficient to maintain the wheel space within a desired temperature range. In such situations it is known to disassemble the turbine engine and remove plugs from the combustor inlet housing. This results in diversion of a portion of the high pressure air exiting the compressor to the wheel space through the openings formerly closed by the plugs. While the result is supplemental cooling of the wheel space region of the turbine, the modification is permanent. As such, cooling air is delivered to the wheel space when it may not be required, thereby lowering the overall performance of the turbine engine.
It is therefore desired to provide a gas turbine engine having improved cooling.